If a picture is worth a thousand words, a three-dimensional model may be worth a million. Computer models, developed on computer-aided design and development (CADD) systems, are used in a variety of industries to help people better understand and visualize the object being modeled, without requiring someone to build that object. For example, architects can generate virtual walkthrough tours of buildings before they are built so that clients can visualize internal spaces and also see how a building might look on its site. Engineers can build whole systems to better see how various parts will fit together. And biologists and chemists can build objects that already exist but that are too small to be seen easily, such as molecules.
Processing of three-dimensional models requires extensive computational capabilities, however. That is because an enormous number of faces on an object may need to be computed (i.e., whether a surface is visible, etc.), as does the way that light interacts with and reflects off of those surfaces. Also, a user may need to install particular software to handle the display of three-dimensional models, such as VRML or Quicktime VR. The model can also be turned into a movie that requires less processing power to display, but in that case, the user may lose the ability to interact freely with the model.